In the fields of semiconductor devices, flat-panel displays, micro electro mechanical systems (MEMS), circuit boards, optical devices, mechanical devices, and the like, various structures with patterns formed on their surfaces are fabricated. In the manufacturing of such structures, various kinds of testing are performed to find whether or not there are any defects such as defective shapes of patterns, defective dimensions of patterns, and existence of foreign objects.
A testing method called the die-to-database method is known as a method of finding defects of patterns formed on surfaces of structures. According to this testing method, defects are detected by comparing test data with reference data. To obtain the test data, an enlarged optical image of a pattern is formed on the light-receiving surface of a charge coupled device (CCD) image sensor or the like. The reference data, on the other hand, are obtained on the basis of the design data (CAD data) used to design the pattern or the like. If there is a difference between the test data and the reference data, then the difference is detected as a defect.
A known pattern-testing apparatus detects defects such as wrong sizes and wrong positions of contact-hole patterns, which are microscopic patterns, on the basis of the sum of the luminance values of the light that passes through an area to be tested (for example, refer to JP-A 7-128248 (1995)(Kokai)).
A photomask testing apparatus to be used in manufacturing semiconductor devices checks whether or not there is any defect, and also sometimes detects line widths of the microscopic line-and-space patterns.
In addition, there is known an apparatus for evaluating the printability of photomask pattern that are printed to the surfaces of wafers by an exposure device. The apparatus picks up an enlarged optical image of the pattern of a photomask by a CCD sensor or the like, using an optical system equivalent to that of the exposure device, and thus detects the transmittance magnitude or the line widths of the calculated wafer plane pattern.
The apparatus capable of evaluating the printablity, however, employs a technique with a limited capability of detecting: the transmittance of contact-hole patterns; and the line widths of the line-and-space patterns. Specifically, the technique only enables detection within a limited area. That is, the apparatus can perform detection at predetermined intervals, but cannot perform detection with high resolution on all over the area of the photomask. On the other hand, some of the apparatuses to test photomasks have functions to acquire the distribution of line widths, but still are not capable of acquiring the line-width distribution with the printablity taken into consideration. Accordingly, characteristics or characteristic profiles of the photomasks (such as, the transmittance profile, the line widths profile with the printablity taken into consideration) cannot be detected from all over the area of the photomask with high resolution.
The patterns on photomasks have been more and more microscopic in recent years. In such circumstances, there is a growing demand to improve detection sensitivity of contact-hole patterns, and to precisely evaluate the quality of photomasks, the cause of the lowering of the process margin attributable to the photomasks, and the like.
The conventional technique to detect the transmittance or line widths, however, is not capable of detecting the characteristics or the characteristic distributions of photomasks. Accordingly, when the process margin or the yield is lowered due to an anomaly not so serious as to be regarded as a defect, the cause of the lowering may not be identified, for example.